1. Field of the Invention
The present invention relates to a rangefinder apparatus for measuring the distance to an object to be measured; and, in particular, to an active type rangefinder apparatus suitably used in a camera or the like.
2. Related Background Art
In active type rangefinder apparatus used in cameras and the like, an infrared light-emitting diode (IRED) projects a luminous flux toward an object to be measured, the reflected light of thus projected luminous flux is received by a position sensitive detector (PSD), a signal outputted from the PSD is arithmetically processed by a signal processing circuit and an arithmetic circuit and then is outputted as distance information, and the distance to the object is detected by a central processing unit (CPU). In general, since errors may occur when the distance is measured upon a single light-projecting operation, light is projected a plurality of times so as to obtain a plurality of distance information items, which are then accumulated at predetermined intervals by an integrating circuit so as to be integrated and averaged.
Also, in such a rangefinder apparatus, since the light received by the PSD includes not only the above-mentioned reflected light component but also a steady-state light component, the latter is eliminated as follows in order to take out only the reflected light component from the light received by the PSD. Namely, the luminous flux is projected from the IRED in a pulsing fashion, and the steady-state light component received by the PSD during the period when the luminous flux is not projected from the IRED is stored in the steady-state light eliminating capacitor in the signal processing circuit. Then, the steady-state light component stored in the steady-state light eliminating capacitor is subtracted from the reflected light component and steady-state light component received by the PSD during the period when the luminous flux is projected from the IRED, whereby only the reflected light component is outputted from the signal processing circuit.